Please refer to FIG. 1 and FIG. 1A, which disclose a computer cursor device utilizing the theorem of electromagnetic induction in the prior art. The computer cursor device includes a transmitting winding coil 2b and a plurality of detecting winding coils 2a. The transmitting winding coil 2b is formed by a single winding, and the detecting winding coils 2a are formed by a plurality of secondary windings respectively. A magnetic element 4 is disposed between the transmitting winding coil 2b and the detecting winding coils 2a. 
When the magnetic element 4 is pressed, the distance between the single winding and the secondary windings is changed, and the voltage outputted by the secondary windings will be changed too. Next, the voltage will be processed via amplifier, filter, scanner, and an analog-to-digital conversion to be a digital signal. Finally, the digital signal will be transmitted to MCU (Micro Controller Unit). The MCU will calculate the digital signal to a displacement quantity and the angular moving direction of a computer cursor. The angular moving direction is depended on the location of the secondary winding, which generates the changed voltage. Because, the more number the secondary windings generate the changed voltage, the more distance the computer cursor moves.
The prior art of utilizing the theorem of electromagnetic induction via the single winding and the secondary windings can control the velocity of the cursor according to the changing quantity of the voltage. However, there are many problems in the prior art needed to be solved. For example, the characteristic of the single winding and the secondary winding are influenced by the material, winding method of wire, and the material of the winding the wire. Even the characteristic is changed slightly, and the voltage will be changed huge. Especially, keeping the quantity of the force pressed down the voltage and the output of the voltage with a constant proportion is a great challenge. Besides, the voltage outputting by the secondary windings will be easily influenced by the electromagnetic generated by mobile phone, family electric appliances, or computer. However, the electromagnetic interference in the computer cursor device is a very hard to eliminate. Therefore, the computer cursor device in the prior art is needed to be improved.